This application claims Paris Convention priority of DE 199 19 497.1 filed Apr. 29, 1999 the complete disclosure of which is hereby incorporated by reference.
The invention concerns a transport device in a packaging machine, in particular a tube filling machine comprising an endless belt guided via at least two deflection pulleys, on the outer side of which a plurality of supporting devices are disposed, one end of each being borne for pivoting on the endless belt via a bolt extending transversely to the longitudinal extension of the endless belt, and the opposite end of which engaging in the neighboring supporting device in a pivoting manner and also for displacement in the longitudinal direction of the endless belt.
When filling and closing a tube in a tube filling machine, the tube must be guided by a transport device through several working stations. The tube is usually borne in a tube holder whose dimensions are adapted to the tube to safely support the tube with tight fit. A so-called oval conveyor is frequently used as a transport means and comprises an endless conveyor belt guided via at least two deflection pulleys or wheels. The conveyor may be a belt, e.g. a toothed belt or a chain. A plurality of supporting devices are mounted, with the mentioned tube holders, to the outer side of the endless belt and circulate with the endless belt. Drive is effected by a driving motor acting on one of the deflection pulleys.
The quality of the filling or closing operations and the functional safety or susceptibility to malfunctioning of the tube filling machine depend essentially on the positioning accuracy of the tubes in the individual working stations. It is therefore important to mount the supporting devices or tube holders safely and with high accuracy to the outer side of the endless belt. The supporting devices must thereby be supported such that, in the deflection region of the endless belt at the deflection pulleys, neighboring supporting devices can exert a relative pivoting motion and also slight displacement in the longitudinal direction of the endless belt to prevent the occurrence of constraining forces and constraining stresses and strains.
In conventional tube filling machines, each supporting device is borne on the endless belt by mounting a bolt to the outer side of the endless belt the bolt extending on the outer surface of the endless belt and being perpendicular to the longitudinal direction thereof. The supporting device captures the bolt within two bores spaced apart from one another by approximately the width of the endless belt to thereby form a pivoting bearing having two bearing points spaced apart across the width of the endless belt. The opposite end of the supporting device comprises one single fork-shaped receptacle which surrounds the bolt of the neighboring supporting device. The bolt can be displaced in the fork-shaped receptacle. In this fashion, a rectilinear sliding pair is formed which can compensate for the length variations between the bolts of two neighboring supporting devices during deflection at the deflection pulleys.
Practice has shown that the rectilinear sliding pair, which usually consists of plastic, wears rapidly with time, since it abuts with the bolt along a relatively small surface, leading to relatively high local stress maxima. Wear is further increased by the fact that lubricants are normally not used in the transport device, since, for hygienic reasons, the open tubes should not come in contact with any lubricant. Moreover, the maintenance and amount of work required for lubricating all joints of such a transport device would be excessive.
The conventional supporting devices comprise a three-point-support with two pure pivot bearings on the bolt, disposed at a distance from one another in the transverse direction, and with a rectilinear sliding pair disposed at the opposite end. Although this provides a statically defined support which prevents constraints, it has however been shown that the spatial stability of such a support is insufficient in certain situations, since the three-point support tends to tilt about its diagonal axis due to the asymmetric arrangement of the supporting points, wherein the lever arm of the bearings is relatively short for accepting the associated torque. It is impossible or very difficult to achieve rigid support of the supporting devices or tube holders in this fashion.
It is the underlying purpose of the invention to create a transport device of the above mentioned type which guarantees precise positioning of the supporting devices over a long operating time.
This object is achieved in accordance with the invention in a transport device of a packaging machine in that the supporting device is connected to the neighboring supporting device via at least one joint plate which is connected to the supporting device for pivoting about a first axis, and which is connected to the neighboring supporting device for pivoting about a second axis parallel thereto.
The joint plate is preferably disposed at an angle relative to the longitudinal direction of the transport belt such that the mutual distance between two neighboring supporting devices can be compensated for by changing the angular position of the joint plate without causing constraining forces. Moreover, the joint plate permits neighboring supporting devices to pivot with respect to one another. Pure rotational motion has more favorable frictional and sliding relationships than does translational motion, so that the wear behavior of the rotary joints in the joint plates is less than that of the conventional rectilinear sliding pair. This considerably increases the service life of the transport device. Moreover, the joint plates substantially increase the spatial stability, in particular with respect to tilting behavior, compared to the rectilinear sliding pair with capturing fork-shaped receptacle. This increases the overall stability of the transport device such that predetermined positions can be set in a reproducible manner with high accuracy. This is favorable for the quality of the filled, closed tubes.
In a preferred embodiment of the invention, each pair of neighboring supporting devices is connected to each another via two joint plates to obtain a four-point support for each supporting device by providing two spaced apart supporting points on the bolt at the one end of the supporting device and two likewise distanced supporting points on the two joint plates at the other end of the supporting device. The joint plates should thereby be spaced apart from one another as far as possible. This can be effected, in particular, by disposing them close to one of the longitudinal edges of the endless belt. The four-point support makes the suspension of the supporting devices exceptionally rigid, wherein the tubes can be guided through the tube filling machine with high precision. Theoretically, a four-point support is overdetermined. However, the support is not subjected to excessive loads since typical modern production tolerances can maintain very small tolerance deviations of the support points from their desired values which, in turn, can be compensated for by the elasticity of the overall system and, in particular, of the endless belt to reduce theoretically conceivable load peaks.
With the four-point support, external forces acting e.g. when inserting and lifting out the tube holder, no longer cause lateral tilting and are largely compensated for by the supporting device, since the lever arm for accepting torques is substantially larger than that of a three-point support due to the mutual distance of the supports.
In a preferred embodiment, the joint plates are directed essentially perpendicular to the longitudinal extension of the endless belt when the supporting devices are rectilinear, i.e. in the area between the deflection pulleys. This permits neighboring supporting devices to be disposed very close to one another with the joint plates requiring little construction space to increase the number of supporting devices in the transport device. In addition, there is sufficient space to compensate for changes in distance due to relative motion between neighboring supporting devices in the longitudinal direction of the endless belt by disposing the joint plates in an inclined manner.
In a preferred embodiment of the invention, the second axis is formed by the bolt of the neighboring supporting device disposed on the endless belt. Use by the joint plates of the already existing bolt of the neighboring supporting device permits realization of the support in a very compact manner and with relatively few construction parts.
Preferably, the bolt projects beyond the supporting device and can engage into a guiding rail in a rectilinear section of the transport device between the deflection pulleys to safely position the supporting device.
Further details and features of the invention can be extracted from the following description of an embodiment with reference to the drawing.